So the pictures are right now in Google Photos? In that case, one option is to just keep them in Google Photos. You can get the Google Photos app for iPhone and just keep going.
If not, if you want to move from Google Photos to the Apple Photos app and maybe iCloud Photos, just install the Google Photos app on your new iPhone, sign in so you can access all your photos. , and then use the Share feature in Google Photos to share them all to your Apple Photos app.