CalNet 2-Step - How to check if a device is blocking the phone call from Duo

iPhone:

Settings app from your Home screen.
Tap on Phone, Messages, or FaceTime. Any one of these three sections will work.
Tap Call Blocking & Identification if you chose Phone. Tap Blocked if you chose Messages or FaceTime.
Launch Settings, tap Phone, Messages, or Facetime, tap Blocked or Call Blocking & Identification
Tap Edit in the upper right corner of your screen.
Tap the minus button (red circle) next to the number or email address you'd like to unblock.
Tap Unblock.

Android:

https://support.google.com/phoneapp/answer/6325463?hl=en

If you don’t want to get calls from a certain phone number, you can block it. When the number tries to call you, your phone declines the call automatically.
Note: Some of these steps work only on Android 6.0 and up. Learn how to check your Android version.

Block a number

1. Open your device's Phone app .
2. Tap Call history .
3. Tap a call from the number you want to block.
4. Tap Block / report spam.

Note: If your phone doesn't have visual voicemail, you could still get voicemails from blocked callers. Learn how to see voicemails listed in your Phone app.

Unblock a number

1. Open your device's Phone app .
2. Tap More .
3. Tap Settings  Blocked numbers.
4. Next to the number you want to unblock, tap Clear   Unblock.

Note: Any calls you got from the number while it was blocked won't show in your call history.

If you can't find a Duo number to unblock, please register another verification method such as Duo Mobile, texts, or passcodes.