The photo was taken with my iPhone.
If you post photos that you took using your iPhone, you can caption it, 'taken with my iPhone' or a simpler way for social media - 'taken with iPhone'.
It is more natural to say 'taken with' rather than 'taken on', you use your phone so the photo has been taken with the iPhone camera.
I snapped this with my mobile
This shot was done on my Samsung phone
If you snap something then you take a photo of something. It may be used as a verb; 'to snap,' or as a noun - eg: a snap. If you take a photograph or make a video clip of something, then it may also be referred to as a shot.
"I took some shots of the scenery."
"I took a lot of snaps whilest I was on holiday."
I took this with my smartphone
I shot this with my smartphone
It's an iPhone photo
'I took this with my smartphone'
We often use this expression when describing this situation.
I.e: I took a photo (took)
'I shot this with my smartphone'
Another option is to say 'shot' instead of the word 'took'. Shot is another photography term for taking a photo.
Eg: 'What a great shot of me at the beach.'
'It's an iPhone photo'
You can also say this simply by directly saying this photo was taken with an iPhone.
Eg: 'I took it with my iPhone.'
Eg: 'I took it with my phone.'
Eg: 'I shot it with my phone.'
I hope this helps :)