When first Raspberry Pi came out 2012, I had a cheapo phone with no USB host capability. Found out however that Raspberry makes phone USB tethering connection automatically. And then if you enable FTPD and in TELNETD in Raspberry you can access it from the phone quite transparently. As an example I could now move videos and photos from the phone to USB hard disk while in the wilderness. Or use TV-dongle in Raspberry and stream it to the phone.