Your phone itself can be used for the recording, but you need to bypass the mic ADC/DAC (most likely), and that's only really practical using the USB bus, so if you only have that option, you'd need maybe a mic preamp with USB out. There are dozens of perfectly decent handheld digital recorders in the $100-200 range with good mics that will handle the entire job. They will probably drive you half-crazy until you get used to them in terms of physical placement and setup for recording, but when properly set up, handled, and configured (WATCH THOSE RECORD LEVELS!) produce genuinely professional results.