I need to sync my photos off my computer to my new iphone

Turn on iCloud Photos on both devices. If you want to save space on the phone, also turn on the Optimize Storage option. See: https://support.apple.com/en-us/HT204264

Also note that iCloud Photos is a syncing service. Any photo you 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.

If your computer is a Windows computer, also see: Set up and use iCloud Photos on your Windows PC - Apple Support