Hello Monique0409,
Thanks for asking the Apple Support Communities for help with your iPhone volume.
It sounds like you are experiencing the Attention Aware feature. If you are looking at the device, the ringer volume will be lower. To test this, have your iPhone face down and have someone call you.
"If you're looking at your device, it will lower the volume sound of your alerts."
If you don't wish to use this feature, you can also turn it off: About Attention Aware features on your iPhone X or iPad Pro - Apple Support
"If you don’t want to use these features, go to Settings > Face ID & Passcode and turn off Attention Aware Features."
You may also want to verify your ringer volume, which can be separate from game or music/video volume. Check your settings using this article: Adjust the volume on iPhone - Apple Support
Depending on your settings, you may be able to use the side buttons while in a call to raise your volume, or you have to adjust it in Settings > Sounds & Haptics.
Thanks and have a wonderful day.