Did you assume that i have an iPhone? I don’t have one and i don’t understand what led you to think so. I said that i use Syncthing to sync my Aegis backups, hence i have an Android phone, because Aegis is an Android app. Though Syncthing can work both ways, also syncing from a computer to a smartphone. It IS a flexible tool.
And judging by the way you have worded your initial question, you are interested in finding a way to filesync on an Android device, thus i suggested Syncthing because it is present on Android. It is not on iPhone unfortunately, at least the official downloads page doesn’t feature a link to the App Store.
And as you said you don’t have a computer, so why am i even going on about it.
Though if you only want to sync Aegis backups, i don’t see much problem with just opening Mega app and manually uploading them once in a while. I assume you don’t add 2FA to a new account every day or even week and you don’t need to obsessively sync every new backup ASAP.
But if you need to often sync many different local files on a phone then i don’t know how to help you, sorry. Doing it manually every time is a soul crushing chore, i understand.