The partial answer is to use "My Photo Stream" on your iPhone. What that does is sync a max of 1,000 photos across all devices but only for 30 days. It's up to you if you want to save those photos stored in the cloud onto your physical device. After 30 days, they will be removed from from the temporary cloud apple has made for you. The pictures you still take on your iPhone will still physically be on your iphone
My Photo Stream FAQ - Apple Support
On your phone & iPad
Go to: settings --> Photos & Camera --> turn on "My Photo Stream"
What this does is: "automatically upload new photos and send them to all your iCloud devices when connected to wifi."
So make sure your iPad has the same apple id as your phone. You can even have it sync to your mac/windows pc.
A couple things to know:
- The photos you upload to My Photo Stream don't count against your iCloud storage.
- your iPhone, iPad, and iPod touch keep your most recent 1000 photos in the My Photo Stream album
- Photos in My Photo Stream are saved on the iCloud server for 30 days. (To save or back up these photos, you must save them from My Photo Stream to your iOS device)
- If turn off My Photo Stream on your iPhone, iPad, or iPod touch, all of the photos in the My Photo Stream album are removed from that device only