cell phone external storage device plus portable charger

I want to make a portable charger with an external hard drive.
example I don't want to fill up my phone with music, videos, movies, pictures etc.
I would like to create a board that can charge my phone and have an external memory.
I would like to know what board is proper to use.

I would like this device to be able to communicate with my cell phone so I can put photos and movies, videos and such on an external drive. Through an app or just connect like an SD card of some sort to where I can transfer files. I want it to be completely be portable so when I'm traveling. I literally can leave my laptop at home.

thats all i would want it to do.

This doesn't sound like an Arduino solution; more of an OTG (on-the-go) USB cable with a storage device attached (eg a 64Gb Flash) which is visible to the phone onto which you can dump the data.

Well, that might work for an Android, not so sure about locked-down Apple. I've used this solution a few years ago but not with my current smart phone.