Four things go wrong, and all four are free to fix
Light first. Photograph your animal near a big window with the light coming across them rather than from behind, and turn the flash off — a flash flattens a coat, throws a hard shadow behind the ears, and gives a dog the eyes of a road sign. A dim room and a flash is the combination behind most of the photos people are quietly disappointed by.
Then get down. A photograph taken from standing height is a photograph of the top of a head, and it is the single most common mistake there is. Kneel, lie down, put the phone on the floor. While you are down there, look at what is behind them, and move a metre sideways so it is a wall rather than a laundry rack. Then make a noise they have never heard before and take the picture in the second that follows.
What a portrait adds that a good snapshot does not
A set. One lucky photograph is one lucky photograph; what you get here is the same animal treated consistently across several looks — a clean studio frame, a monochrome that suits a black coat, a warm one from low sun, a painted one — all recognisably the same treatment, which is what makes a row of them work on a wall or a card.
And staging you cannot do at home. A seamless backdrop, a rim of low evening sun through the coat, side light raking across fur to hold its texture: these are lighting setups, not filters, and the reason they do not happen in your living room is that your living room has one window and a radiator. The output is also sized for print rather than for a phone screen.
The photos on your phone are the raw material either way
This is the part that ought to make the page trustworthy rather than the part we hide. Everything generated here is built from photographs you took on a phone, which means the advice above is not an aside — it is the instruction manual. Three to twenty recent pictures, taken at eye level in daylight, from a few different angles, produce a gallery that looks like your animal.
The inverse is also true and worth saying plainly. If every photo you own is a dark shape on a dark sofa taken from the doorway, no amount of processing invents the coat detail that was never captured, and the result will be a portrait of a dog that is nearly yours. Spend ten minutes by the window first. That ten minutes is worth more than the pack you choose.
How to decide when the free option is enough
Ask what the picture is for. If it is for you, or for one person you are sending it to this afternoon, the phone in your hand is almost certainly enough, and the honest advice is to go and use it while the light is good. Nothing on this site is faster than a camera you are already holding, and a photograph of a real moment has something built into it that a portrait does not.
If it is going on a wall, onto a card that fifty people will open, or into a frame for somebody else's shelf, the questions change. Now you want several looks to choose between, consistent handling, enough pixels to print, and no dependence on whether the animal happens to sit still this afternoon. That is the job this was built for, and it is a narrower job than the phone's.