The difference between a mobile phone and other objects in a dream is that it literally represents your connection to the world - contacts, information, online identity. I agree that work stress is a common cause, but the specific pattern of theft rather than simply losing the device suggests something more: fear of losing control over something that belongs to you, not just disconnection. The fact that you end up "completely lost" and unable to contact anyone points to an anxiety about vulnerability, not just generic stress. This usually passes when you resolve what's actually putting you in that situation - sometimes it's not work itself, but feeling adrift about decisions you've made or that you feel slipped away from you.