I don't think Gimp is the best one for photo editing. I like photography and often take photos with my camera. I would like to edit photos on my iPhone. The apps VSCO, Adobe Lightroom, Picsart, Snapseed are my favorite. VSCO is stark for its filter feature. Picsart is a fashionable one. Snapseed...
I think you can save it on your phone by recording the streaming video and audio. If you use iPhone, you can use the default ios screen recorder. And for Android phones, you need to install one screen recorder app on it. Just record it while playing back.