Deleting photos from android phone

[WutheringFrights]

I have an immensely stupid question to ask...
My android phone saves photos (syncs?) to Google Photos.
If I delete photos off my phone will they still be on Google - or do I have to do something to make sure it doesn't sync and delete all those too?
Its utterly ridiculous - I have 4500 photos!
I'm fairly sure that's why my phone hates me (well that and the totally fubarred screen...)