how to transfer my photos in my phone to my ipad?

Do you sync photos with iCloud?

Settings

Tap Your Name

Tap iCloud

Is Photos turned on?

If yes and you use the same Apple ID on your iPad, you do the same there and your photos will sync with all devices using the same Apple ID and where Photos in iCloud are turned on.

iCloud is not a true archive backup service. It is a Syncing service. If you delete a photo you sync with iCloud on one device, it will delete on all devices including in iCloud. To ensure you don't lose your photos, you might want to backup your photos to your computer or use a 3rd party backup service, like Dropbox, Carbonite, Google Photos, Amazon Photos (if you're a Prime member).

If you want to transfer your photos to your computer for storage, this link will explain how to do that --> Transfer photos and videos from your iPhone or iPad to your Mac or PC - Apple Support

Finally, make sure you are backing up the data on your iPhone, since you admit it is now having issues. This link explains how to backup your iPhone --> Back up iPhone - Apple Support

Log into one same Apple ID for both iPad and iPhone and send the photos using AirDrop, or just sync with iCloud if you store them there.