If i put off icloud photos being backed up on icloud drive, will i get my pictures back if i change my phone?

If you turn on iCloud Photos and allow time (may take a few days) for all of your photos to sync with iCloud as described in See instructions in Set up and use iCloud Photos - Apple Support

and then erase your phone as described in What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

your photos will remain in iCloud Photos (not iCloud Drive) and they will sync with your new phone when you set up iCloud Photos on it.

Be aware that iCloud Photos is a syncing service. Any photo you manually delete from a device where iCloud Photos is turned on will also be deleted from iCloud and from any other device connected to iCloud Photos. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See: Set up and use iCloud Photos - Apple Support