Need more free space on your mobile phone?

Try Google Photos

All you need is a google email account
Install the app on your iOS(Apple) or Android device
You can set the photo/video quality to:
high(unlimited space on the cloud)
or original(limited to your cloud space for example 15GB on Google's free account)
This will be asked when you run the app for the first time

I make use of the high(unlimited)

Here is how it works:

Open the app.
Make sure you are connected to your wifi connection.
Backup of all your photos in your phone's gallery will automatically upload.
Click on the menu icon on the top left.
Click on "Free up space".
Select Delete ( It will only delete files that are backed up, no need to worry that you would lose photos)
Exit the app and go to you phone's gallery or photos
Go to deleted times
Select all and delete (empty recycle bin) Alternatively you can leave your deleted items here and they will be automatically deleted after 30 days.