Claire is correct. The phone number displayed on your listings is pulled from your Trulia profile, so you'll want to edit your profile to change it. To do that, access the link below to navigate to your main profile page. Then, select 'Edit Profile' on the left. Under the 'Personal Information' section, you should find the option to update your phone number.
Let us know if you need any further help. You can always feel free to contact our Customer Service team either by phone at 888-466-3501 Monday - Friday 7am to 4pm PST, or by email via http://www.trulia.com/help/ask/.