Your dealership has the choice between two options for email signatures: Store Default or Personal Signatures.
For stores with a store default email signature format:
You will need to speak with the expert user at your store to have the store format modified to not include your cell phone number.
For stores with a personal email signature format:
You can modify your personal email signature using the Email Signatures menu in My Settings. See Email Signatures for detailed instructions.
How do I know which email signature format my store uses?
Reach out to your customer success team and we can verify that information for you!