Play Store missing from my android phone, how do I get it back?

It's almost always disabled rather than gone, you can't properly uninstall it on a normal phone. Settings > Apps, show system apps (it's in the three dots menu), find Google Play Store. If there's an Enable button, tap it and the icon comes back. If it already says enabled, check your launcher hasn't hidden it or tucked it in a folder. Don't go downloading the Play Store from random sites.