If you’re never quite sure when your iPhone media is going to sync up with your iPad media and it seems to take forever before it does, here’s what I do.
I AirDrop. I don’t sync my iPhone photos to my IPad via iCloud (i.e., Under Settings/Photos, iCloud Photos is turned off).
When I want a copy of my iPhone media on my iPad, I select the specific media that I want and then Airdrop it to my iPad. This is fast and doesn’t clutter up my iPad with iPhone media that I don’t need.
Unlike my iPhone, I do have my iPad sync'ed to iCloud (i.e., Under Settings/Photos, iCloud Photos is turned on). That means that any media that is added or deleted from my iPad is also added or deleted from iCloud. This also allows access to this media from other iDevices that are sync'ed to iCloud or from a laptop.
AirDrop used Bluetooth and works when your iDevices are close to each other. It doesn’t require WiFi or cellular. If you’re not familiar with AirDrop, read this. https://support.apple.com/en-us/HT204144