iPhone saying not backed up.

[Alfiemoon1]

Plugged my iPhone 6s into the laptop and did a back up last week it confirmed it was done yet it keeps flashing on my phone that it hasn't been backed up for 18 weeks buy more storage It's a new phone and I don't get all this i cloud etc I had an I phone before and just ignored the messages but it's getting annoying

It may be that you haven't enough iCloud space, have a look in the settings at the iCloud storage to see if you are at the limit. If you haven't bought any it is 5gb which you get free, you may need purchase some, it is 79p a month to take it up to 50gb

When you plugged it into the laptop did you back it up to that or to iCloud

I don't get the difference between I cloud space and phone storage what goes on the I cloud and what goes on the phone

The cloud is where the phone backs up to. You can decide which of your apps backs up associated data.