Hi there Katrinella,
Thank you for posting in Apple Support Communities!
We'll be glad to look into these volume issues on your iPhone. Let's start by testing some settings.
Go to Settings > Sounds & Haptics. Make sure the slider is to the lowest setting, and then try listening to the meditation. Does that sound quieter?
If you adjust the volume using Control Center, does that make the sound quieter? More information is here: Adjust the volume on iPhone
Does this happen while you're using headphones? If so, please try using different headphones and test.
Is there any improvement if you power off and restart? Restart your iPhone
Have a great weekend!