How can I delete the pictures stored on the On My Mac section of my photo library on my iPhone?

Simply create a new empty folder on your PC and Connect your phone, open iTunes, connect, and sync that with Itune software.

The Photos in the section "From My Mac" have been synced to your iPhone from a computer, either with iTunes or the Finder on a Mac. You cannot delete synced photos directly from your iPhone. They can only be deleted by syncing the iPhone again with a computer and deselecting the previously synced albums. The new syncing will replace all previously synced photos with the currently selected albums for syncing.

A quick and dirty way to remove all synced photos at once would be to enable iCloud Photos, just temporarily. As iCloud Photos is incompatible with the manual syncing iCloud will remove all synced photos, when you enable iCloud Photos. If you want to try this, do not enable "Optimize iPhone Storage", when you enable iCloud Photos. Otherwise iCloud might remove some of your original photos from the iPhone and keep them only in iCloud. Uncheck"Optimize iPhone Storage", when you enable iCloud Photos. Wait for the synced photos to bereaved, then disable iCloud Photos again.

You're welcome, tokyofroodle and kmanomai 😊

You're welcome 😊

AHHHH THANK YOU!!!!

thank you so much. (^o^)