That printer can only be used to print from phones via Bluetooth if it's got the optional BU-30 adaptor attached to it. They aren't easy to get hold of for such an old printer and, if you can find one, you'll probably end up paying far more for it than for the printer:
https://shop.bt.com/products/canon-bu30-bluetooth-adapter-ip100-2553b003aa-83Q0.html
Without that adaptor, a PictBridge compliant camera or phone can be connected directly to the printer via a cable. (I tend to associate PictBridge more with cameras than with mobile phones though. There may not be many phones that support PictBridge).
For instructions for either of the above methods, download the on-screen manual from here:
https://www.canon.co.uk/support/consumer_products/products/fax__multifunctionals/inkjet/pixma_mp_series/pixma_mp620.html?type=manuals&language=#DLInstructionDiv
[It's an executable file. You need to run it to install the manual as a program onto your PC. The relevant section is located as follows:
MP620 Series Basic Guide > Other Usages > Printing Photos Directly From Your Mobile Phone or Digital Camera].
I'd find it far easier just to download the images from the phone to a PC or laptop and print from there!