The Voice Memo app on iPhone has the built-in feature to allow users trim down voice recordings right on the iPhone. Sometimes however we may want to do the opposite, combing two or more voice memos or sound recordings into one file. There are basically two ways you can achieve that. You can export the recordings to a computer, then merge the iPhone voice memos on your PC or Mac.
Alternatively you can download an audio editing app for iOS to join the voice memos together on iPhone. Hokusai is a free audio editor app that can mix or merge multiple audio clips, sound tracks on iPhone. Here’s how it works.

Merge voice memos on iPhone
Run the Voice Memos app, tap Edit button at the top right corner, choose the sound recording, tap Share, choose Save to Files, select a folder and save a copy of those selected voice memos to the Files app on your iPhone.

Download the free audio editor app for iPhone. Then create a new project in the audio tool. Tap the Import button at the bottom to browse to the voice memos saved in the Files app and add the first voice memo or audio recording track to the audio editor. Then move the playhead to the end point over the horizontal, time-based sound wave of the first audio track. After that go to import the second voice memo or sound recording from Files app to the audio editor. If you need to add extra sound tracks, make sure to drag and drop the playhead to the end of the previous audio.

Optionally you can also play any added sound tracks and trim the audio or music to remove the unnecessary audio segment before you merge them.

Tap the spanner icon at the top right section, select Share Audio from the drop-down menu, save the merged audio to the Files app on your iPhone, any cloud service you use. You can also share the merge music/audio via message, mail, chat apps and more.
How do I join 15 voice memos
I needed this for an IRP (Independent Reading Project (book report)) and it is pretty good!
seems the app isn’t in the app store anymore. 🙁
you can get the app download link from this page.
How do I import the finished product back to the voice memo app after I’m done combining.
sorry, you can export voice recordings from the Voice Memos app to other apps, but can’t add audios or recordings from third-party apps back to it.
Hi – so if I download the Hokusai app, move my recordings to it and merge/edit, how do I then get the finished product to my laptop?
Tap the spanner icon at the top right section of the Hokusai app to bring up the menu(see the last screenshot in above post), select Share Audio and choose your preferred tool to send the audio from iphone to other devices. If you have an email configured on the phone, you can send the audio to yourself, then open the email from your computer.
How do I drag the audio in Hokusai?? It doesnt let me DRAG my audio to match the other audio.. 🙁
with the free version of the audio editor, you can’t drag the audio in timeline. however if you put the playhead at the end of the first track first, the send track will be imported and append to the end of first audio track automatically, no need to manually drag the audio.