Here’s wishing loads of joy and happiness making music with the new guitar, Swashata.
Guitar sounded pretty good in the Zombie play through, as did your playing. Lots of energy, solid rhythm, clean chords.
Something to perhaps experiment with, based on a tip I picked up on from Justin’s Strumming Techniques video, is trying to vary the strength of your grip on the pick to add dynamics. Tighten the grip for extra volume, relax for less, all with the same strumming action.
I assume you were playing through the acoustic amp voicing on the BK50?
Before considering a mic for you phone, I would suggest trying to make your videos using OBS on your laptop and OBS Ninja that feeds phone video to OBS. You can read about it here. If I recall correctly you can feed audio direct from the BK50 via a USB link to your laptop, which could then be routed to OBS. If I am right about feeding audio direct from the BK50 then this solution would solve an immediate need to improve audio quality (I think it would deliver better audio than the phone mic recording the amp)
The reason I suggest that, is that you can then consider alternatives to an external mic for the phone, which I think would give you more mileage long term. If it works for you to make videos that way then you could get either a USB mic to record either the acoustic guitar or the BK50 or consider an audio interface and mic.
Going that route, in time, would allow you to make multi-track recordings in a DAW (Digital Audio Workstation). You may not want to do that now, but in time, you may enjoy doing that (I know I do).