How can I increase my iPhone's storage space?

And good morning. In regards to the topic above, does anyone know how I can increase my iPhone's storage space? What I'm looking for, specifically, is a means of transferring [video game] app data, externally, while I continue using the app.

In essence, I would ideally be streaming data between a gaming app and an external storage device.

Kind regards,
Otaku

P.S. I've heard and seen an iPhone flash drive in action. But I'm unsure of whether or not it can simultaneously "steam" data between the gaming apps and the flash drive.

If they are cable of such, does anyone have any recommendations?

You can increase the storage buy using an OTG device and the relevant software. Otherwise, don't buy an iPhone as every single one does not have expandable memory which is stupid nowadays.