Can I add more storage to my cellphone?

Sorry but no.

Storage can’t be added after the phone is manufactured.

That said, see this article on how you might be able to better use whatever on-device storage you DO have:

How to check the storage on your iPhone and iPad – Apple Support (AU)

Hello ~ Taking a look by clicking on the helpful link below and reviewing the information there…

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

As for the lol ….

~Katana-San~