This is probably a long shot, but does anyone know where I could find an English translation of the phenqitho?
LOL. AFAIK, it doesn't exist. The closest thing to it is a three volume adaptation published by the (Syro-Malankara Catholic) monastery "Kurishumala Ashram" in Kerala. I say adaptation rather than translation because it is a version intended for use in that particular monastery and so it has its own quirks. You can probably obtain it from them.
From an initial Google search, it seems that it has fallen out of popular use, and thus has not been translated, but you never know. Even an abridged version would be nice.
I don't think it's fallen out of use per se, just that wherever it is used it is used in Syriac. It more or less fell out of use in India during the transition to vernacular liturgy (if not before).
I'm planning to purchase Bede Griffiths' translation of the Sh'himo when I have the funds.
SEERI publishes a book called Awsar Slawoto
which is basically Griffiths' translation of the Sh'himo with the Syriac text on the facing page. You might be able to order it from them and I imagine even with the international posting it may be more affordable than buying from Gorgias Press.