How to get space on my iPhone

1.

Try to free up iPhone 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

2. 

What's the difference between device storage and iCloud storage?

What's the difference between device storage and iCloud storage? - Apple Support

See this Apple article: Upgrade to iCloud+ -> Upgrade to iCloud+ - Apple Support

See also: iCloud+ plans and pricing -> iCloud+ plans and pricing - Apple Support

Manage your iCloud storage -> Manage your iCloud storage - Apple Support

You can check what is taking up your iPhone's internal memory here:

Settings > General > iPhone Storage

From there you can also clean up, and delete the content you don't use.

If you lack space in iCloud, you can also consider purchasing an iCloud+ plan. But remember that you will not get more space internally on your iPhone by purchasing more space in iCloud. Apps, photos, music etc. will still take up space in your iPhone's memory. iCloud will just be extra space where you can have all your stuff backed up.

You can read more specifically what the difference is between iCloud and Internal Storage here:

What's the difference between device storage and iCloud storage? - Apple Support

If you want to buy more space in iCloud and upgrade to iCloud+ see here:

Upgrade to iCloud+ - Apple Support