Which programming language for Desktop Version + Mobile version

Hi guys.

I’m about to start working on a website for mostly family use that basically allows photo uploading/storage/display etc, and I want to make it usable on mobile (take photo -> upload to users page/gallery etc) after I get it going on desktop.

I know php/mysql only. Never dealt with anything mobile whatsoever. Do I need to use a certain language/s for the desktop version, to make the mobile version possible? If so, which?

Thanks for your time.