Flip the Ring/Silent switch on the side of the iPhone toward the back of the device
If your iPhone has an Action button, set it to Silent Mode and press it
Open Control Center and tap the bell or sound icon if available
Go to Settings > Sounds & Haptics and turn off Change with Buttons if needed
Turn on Do Not Disturb in Settings > Focus or from Control Center
Lower the ringer volume to zero using the volume buttons or Settings > Sounds & Haptics