My phone only had 6 gb of free space & I think the update requires 5gb so maybe that was the cause.
You need about 7 GB device storage, see this Apple articles below:
If you need more space for an update on your iPhone, iPad, or iPod touch
If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support
How to check the storage on your iPhone, iPad and iPod touch
How to check the storage on your iPhone, iPad and iPod touch – Apple Support (UK)
Clear Other storage on your iPhone or iPad
Clear Other storage on your iPhone or iPad - Apple Support
What's the difference between device storage and iCloud storage?
What's the difference between device storage and iCloud storage? - Apple Support
You can alos transfer photos and videos to your Mac, See the following Apple articles:
Transfer photos and videos from your iPhone, iPad, or iPod touch
Transfer photos and videos from your iPhone, iPad, or iPod touch to your Mac or PC - Apple Support
Transfer images in Image Capture on Mac
Transfer images in Image Capture on Mac – Apple Support (UK)