! Sign on photos

Hi Confused in Wales,

Welcome to the Apple Community.

Re ! Sign in grey circle, bottom RH corner.

Sign may mean you need to download the photo(s) from iCloud.

seems your iPhone may be low on power, or be in low power mode,

and / or

there may not be enough storage for all your photos to be displayed.

Apple support have articles online (links below) that may help.

How to use Low Power Mode to save battery life on your iPhone:

When Low Power Mode is on, the battery in the status bar will be yellow.

You'll see   and the battery percentage. 

After you charge your iPhone to 80% or higher, Low Power Mode automatically turns off.

Complete article: https://support.apple.com/en-us/HT205234

How to check the storage on your iPhone, iPad, and iPod touch

https://support.apple.com/en-us/HT201656

How to download iCloud photos and videos

https://support.apple.com/en-us/HT209454

If needed:

There is also a two-page discussion thread about the ! sign on Photos:

https://discussions.apple.com/thread/7659968?page=1

Hope this helps you :-)