Thanks for posting in the Apple Support Community. I understand you want to increase the volume of your ringtone.
To increase the volume, you can quickly change this by using the volume up/down buttons on the side of your iPhone. Pressing the up button will raise the volume. You can see more here:
Volume up/down: Use to adjust the volume when listening to music, watching videos, or playing games. When you press the buttons, you'll see the Volume under the indicator. When you're not using other apps, the buttons will adjust the ringer volume and you'll see Ringer under the indicator.
About the buttons and switches on your iPhone, iPad, or iPod touch
You can also go to Settings > Sounds & Haptics and change the volume slider to increase or decrease the sound.
Sounds and haptics - iPhone User Guide