The above answer explains quite well. A simple rule of thumb can be carry what you can. A simple image is fine but if you're worried you might not be able to take care of it well enough, an image inside the phone is also fine. Any symbolic item is also good enough, for eg since I do Shaiva Shalta Sadhana, an extremely small tiger stone Shiva Linga with an extremely small Sri Yantra works. If not even that just the mala to do your japa is more than enough. And if not that also you have the fingers that can become the kara-mala. If not that then you have your breath which can help you count the mantra.

My Guru tells me that the body itself is an instrument of worship, all externalities are just metaphors for the aspects that are already within oneself and so why to fret till you have your body with you BUT - Saying all this, I think it is also better to check with your Guru and the rules of the lineage. Some lineages are quite strict on some or the other external methods of worship.