Voicemail volume low

Hello mysato,

Thank you for using Apple Support Communities! I understand that you're wanting to know how to increase the volume of voicemail playing on your iPhone. I would be happy to help provide steps to do so.

While the voicemail is playing, you can use the Volume up/down button on your iPhone to adjust the volume level:

1. Check your voicemail on iPhone - Apple Support
2. About the buttons and switches on your iPhone, iPad, or iPod touch - Apple Support

You can also tap the speaker icon while your voicemail is playing to switch the playback of your voicemail from the iPhone receiver to the speaker. If you find that you're still not able to hear voicemail play at an acceptable level, here's some steps to take next:

If you can't hear a person on a call or voicemail or if the sound isn't clear on your iPhone - Apple Support

Cheers!