Eliza Kelley joined late in the production after the actress who originally portrayed Layla had to drop out due to the more demanding schedule of a feature film. The original actress can be seen in early promotional materials and in the film's early teaser released in late 2020.
The only footage from the proof-of-concept that made it into the finished film was the canal sequence between Isaac (Wan DraL) and Miles (Justin Meyer). The rest of the proof-of-concept was either re-shot or discarded.
Lost Phoenix started as a proof-of-concept short that was shot in late Oct / early Nov 2020. It was initially going to be finished and submitted as a short to festivals before the director decided to skip that and move forward on the full length feature version.
Due to the film's limited budget, many sequences from the script needed to be changed or consolidated to fit the available locations and resources.
Justin Meyer was only available for the proof-of-concept shoots. Anytime you see his character outside the canal, he is being doubled by another actor. Overall, he is portrayed by 4 people (including 3 stand-ins)