Recording an interview on your smartphone using the default smartphone app is not complicated, but you may not always be happy with the result, as native voice recording apps do not usually offer many audio settings.
While you might not care about getting broadcast-quality audio if the recording is just for transcription purposes, later down the line you might also realise a quote from said interview could add more value to the story in audio format rather that in writing, so aiming for clean audio from the beginning can save you time.
Dan Kennedy, associate professor in the School of Journalism at Northeastern University, has shared his digital recording toolkit on Storybench, which aims to make recording and transcribing interviews easier for journalists.
For recording, he recommends the iTalk app paired with a lapel mic, which will provide good quality audio even in a noisy scenario, and several transcription software options, such as Casting Words, Trint and Express Scribe.
Always make sure your interviewee knows if the recording is for notes only or if you are also planning on publishing the audio track.