Smartphones provide large amounts of personal data, functionalities, and apps and make a substantial part of our daily communication. But during phone calls the phone cannot be used much beyond voice communication and does not offer support for synchronous collaboration. This is owed to the fact that first, despite the availability of alternatives, the phone is typically held at one's ear; and second that the small mobile screen is less suited to be used with existing collaboration software. This paper presents a novel in-call collaboration system that leverages projector phones as they provide a large display that can be used while holding the phone to the ear to project an interactive interface anytime and anywhere. The system uses a desktop metaphor user interface and provides a private and a shared space, live mirroring of the shared space and user defined access rights to shared content. We evaluated the system in a comparative user study. The results of the user study highlight the general benefits of synchronous in-call collaboration and in particular the advantages of the projected display and our developed concepts. Our findings inform future designers of synchronous remote collaboration software for interactive surfaces.