How do I increase my disks storage space on iPhone 14+

You cannot increase the amount of local storage (device storage) on any iPhone. The amount of storage that the phone has when it rolls off the assembly line at the factory is the amount that it will have forever.

You can buy (rent) iCloud+ storage space, on Apple's servers, for backups and for synchronization. If you're using iCloud Photos, you can turn on "Optimize iPhone Storage" to let the phone store low-quality / space-saving copies of photos (that it selects) to free up some device storage space. (Full-quality copies remain in iCloud.)

If you have deleted photos and videos – but have not yet permanently deleted them (by waiting 30 days or by going into the Recently Deleted album and deleting them from there), they will take up space until you, or the iPhone, take the final step to permanently delete them. Permanently deleting them means, of course, that if you do not have any copies elsewhere, and later regret deleting the pictures, you do not get them back.

What's the difference between device storage and iCloud storage? - Apple Support

You cannot add any more storage to a phone. If you need more space, you will need to delete whatever you don’t need anymore.