TFM spells out any word it can't make sense of according to its rules - it seems to have a big dictionary which it consults, because sometimes it even pronounces foreign words in the foreign way rather than the way you would expect them to be pronounced using standard English. Actually I can't figure out quite how it works - for example it "spells out" the simple word "nom" even though you would expect it to pronounce that with no trouble using standard English pronunciation rules.
The problem you named, of pronouncing "call" as "cal ell" (evidently) may result from having a space between the two l's - hard to see on the screen. I have frequently had this problem, of a space somehow getting inserted inside of a word, which then makes the word (words!) unfamiliar to TFM, so that TFM spells them out. Annoying, and I can't understand why the space gets in there.