iCloud Photos not syncing
The Photos app usually tells you what's wrong, if you know where to look.
What's usually going on
iCloud Photos pauses itself when iCloud storage is full, the phone is in Low Power Mode, it's on cellular data, or the battery is low. Sometimes it's simply been switched off on one device. Until it catches up, new photos exist only on the phone that took them.
Worth trying first
Read the status.
On iPhone, open Photos and look at the top or the bottom of the Library. A line there says whether it's syncing, paused, and why.
Check iCloud storage.
In Settings, tap your name, then iCloud. If storage is full, photos stop uploading. Free space or upgrade the plan.
Make sure it's turned on.
In Settings, your name, iCloud, Photos, check that Sync this iPhone is on. Do the same on every device that should show your photos.
Give it Wi-Fi and power.
Leave the phone plugged in on Wi-Fi overnight, with Low Power Mode off. Large libraries can take days to catch up.
Confirm on the web.
Sign in at icloud.com and open Photos. Recent pictures there means they're safely stored.
When to hand it over
If photos have been missing for weeks, the library is very large, or photos are spread across several family accounts and devices. We'll find where everything is and make sure there's a second copy.
Your own technologist, on call.
Tell us a little about your setup. We'll take it from there.