We all know that it is hard for a smartphone camera to beat DSLR, but do you need a DSLR that is the question.
Let's start with the question, what is a DSLR camera?
DSLR stands for Digital single-lens reflex camera. But that doesn't tell you anything. In a DSLR, there is a lens which let's light into the camera. The light is allowed to pass to the viewfinder via a prism or a set of mirrors (reflex comes from the reflection here).
This is how you see the image when looking at something you want to take the picture of.
When you press the button to take a picture, the mirror moves out of the way, and the light strikes the image sensor or the film (if it is an old film based dslr). This is how a picture is taken.
You see that is the problem with DSLRs. They are complicated. And there is a huge learning curve. And you need to know this if you want to take a picture.
But on a smartphone camera, you don't need to know this.
Comparison between a DSLR and a smartphone camera
Learning Curve
In a smartphone camera, it is pretty easy to take a picture. Just point the phone at whatever you want to take a photo of and take a shot.
Things are widely different when it comes to a DSLR. Yes you can take a picture in auto
mode, but then that's not why it was made.

To take a picture in a DSLR you need to know things such as shutter speed, ISO, f-stop, white balance and so on.
Whereas in a phone camera, focus and shoot.
Winner: smartphone camera
Image Quality
Image quality is defenitely better in a DSLR, there is no arguing that point. All the tweaking and turning you learned need to be put into use thought.
The DSLR has a huge sensor that is excellent at taking pictures. The sensor on the smartphone on the other hand is a smaller one.

This is because, it is impossible to cramp all the stuff the phone does plus the sensor.
Most of the stuff the image in a phone does is post processing.
You might have seen images where the background is blurred for the person. On the DSLR this happens because of something called aperture
size.
On iPhone and other phones what happens is, after taking the photo, machine learning algorithms blur the background. If you look closely you'll see that there's some issues like space between hairs not getting blurred and all.
Winner: DSLR
Fast moving images
All the images which comes blurred in a smartphone camera can be taken on a DSLR without any distortion.
You might have seen those sports photographers, holding a long lens'ed camera to take a picture, there is a reason to all that.

In a DSLR, you can adjust the time for which the light enters the lens. So let's say you let the light enter the sensor for 1second. This means that if the person has moved in that 1 second, the image will be blurred.
The solution is to quickly open and close the sensor. In a DSLR, you can adjust the time for which the shutter remains open and the time for which light enters the camera. You can have shutter speeds of 1/4000 or even 1/8000 of a second, which means the image will be still.
Also you can take images like this on a DSLR.

This was taken by keeping the shutter open for a longer time and letting light enter the lens for a longer time. This happened because a car came and went, but since the shutter was open for a long time, the light left a trail.
Winner: DSLR
Portability
DSLRs are not exactly what you call portable. They are very bulky devices which you have to carry around.
Unlike a phone which takes care of entertainment and communication, DSLR does nothing and adds to the weight.

It doesn't make sense to carry around a DSLR when you're going out for tea or coffee with your friends. A smartphone camera is what you need at this point.
Winner: smartphone camera
Zoom
You cannot zoom on a phone camera. Some might argue with me, 'hey, I have zoom on my smartphone camera'. Yes and no.
What you have on your camera is digital zoom. Which means the phone just crops the sides of the image and shows you a larger image.
This in turn causes the quality of the photo to decrease as you zoom.

On a DSLR on the other hand, zoom works because of the distance between two lenses on the camera is increased or decreasesd. This means none of the details is lost. You'll get same quality pictures whatever the zoom is.
This is why wildlife photographers are seen having long cameras with them. These cameras have what is called a telephoto lens
which can zoom to great distances by increasing the space between the lenses.
Winner: DSLR
Flash
You can get external flashes for phones also. So I don't think you can say DSLR has got a great flash.
But there are more options here for DSLRs.
Xenon flashes that are compatible for phones are hard to lay hands on.

The flash on a mobile phone is an LED flash and that is nowhere near as bright as the flash that comes attached with the DSLR.
Winner: DSLR
Data Transfer
If you're with your friends, the first thing they're going to tell you after taking the picture is give me a copy.
If you've a DSLR, it might be a bit of a hazzle. Even though modern day cameras come with features like wifi, and you can connect your phone to the DSLR and copy images, it is still difficult.
On a phone you just have to start bluetooth and share it or share it via Whatsapp or Facebook or a similar platform.
Winner: smartphone camera
Versatality
With a DSLR you can do a lot of things which you can't do on a smartphone.
You can change the lens to zoom more or less.
You can change to better lens.

You can take photos with fisheye lenses and similar other crazy stuff.
All this is not doable on a smartphone. You've to live with what you got until you get a new phone
Winner: DSLR
Cost
This is one of the major things that is to be taken into consideration while buying any product.
DSLR cameras are extremely expensive and they only one duty. Unlike mobile phones which can do a ton of tasks and cost relatively lesser than DSLRs.

A top quality DSLR const north of a lakh and when you add extras like lenses it is going to be far above that price. On comparison, the best phones cost around 1 lakh and doesn't need any additional bits and pieces.
Winner: Smartphone Camera
Conclusion
So to the question which is the better camera, a DSLR or a smartphone, the answer is: it depends.
Do you want to dedicate time and energy into learning photography and make high quality photos which you are proud of? Get a DSLR.
If you're into casual photography, and takes photographs when you go out with friends only. A smartphone camera is more than enough for you.
Unless you have a specific need where you couldn't take a shot and you find yourself thinking, 'if only I had a DSLR', get a DSLR. Believe me it will be worth it.