It's not clear what you situation is and what you're asking. For instance, how many pictures do you have? For some Libraries, 19GB would be normal, and for some that'd be really out there. Which is it?
What does your Photos Library look like at iCloud.com? Are all the pictures there? How much storage is used there?
In Settings>[name]>iCloud>Photos, have you turned on "Optimize Storage?"
If you set a device to "Optimize Storage," then Photos may store only smaller images on the device and rely on iCloud to keep the full sized images. This is great, since with the lower resolution images you can scan through pictures very quickly, and they look great on the screen. And, if Optimize is chosen, and you want to edit or crop a picture, Photos will reach out to iCloud to get a full sized image for you to work with. An optimized Library may take up less than 20% of the space of a fully downloaded Library. On my iPhone, Photos takes up way less than 10% of the space it uses on my Mac.
Be sure to keep at least 13 GB free on you phone. Passing 115 GB will begin to cause crazy stuff to happen.
Let us know…