The GTX330ES broadcasts on the 1090 band and the Stratus 1 and 1S receive only on the 978UAT band. Because of this, you will likely not see the ADS-B ownship line populated within ForeFlight Mobile.
To correct this, you will want to check that your GTX330ES is configured to request traffic information be broadcast to you only on the 978UAT band. This will ensure you get the most complete traffic picture from the ADS-B ground stations.
Traffic information set up to be broadcast only on the 978UAT band for use with a Stratus 1 or 1S
If you do not have a GTX330ES manual or are not comfortable with the various menus, you may need to contact your avionics shop to get help setting this up.