Wow, buying a phone so you can carry around an interface just to record guitar and vocal seems REALLY crazy. As Dave suggested, a DR-40 or Zoom h4 or H6 can be had for $200 or less, is self contained (no interfaces needed), and will record in multi track mode. When I used to travel for work, I had my H4n in a little case. It had the power supply, and earbuds. In a pinch, I could put my H4n in my guitar case with a cord and earbuds.
The Fostex seems really dated, and using FAT16 for storage is a limiting factor. Most current recorders use FAT32 and SD cards which are much cheaper and have larger capacities. I only have two things that still use a CF card, a camera and a VERY old RCA mp3 player that was replaced by a cheap MP3 player for about $15. Both sit in a drawer now.
While phones do a lot of stuff great, I can't seeing using one as a "studio recorder". There are much better oo