Learn Portuguese (Portugal): Eles discutiram o problema pelo telefone. - They discussed the problem over the telephone.

Discutiram is the past tense (they discussed) of the regular verb discutir. In the simple past tense, regular verbs ending in -ir drop the ending and add -iram for eles, elas, and vocês.

How is this different from saying 'they discuss' in the present tense?

In the present tense, regular -ir verbs use the ending -em for the 'they' form, making it eles discutem. Because this sentence is in the past tense, it uses the past tense ending -iram, making it eles discutiram.

Since problema ends in an 'a', why is it o problema instead of a problema?

Problema is an exception to the usual rule that words ending in 'a' are feminine. Many Portuguese words ending in -ma (like o programa or o sistema) originally come from Greek and are masculine, so they take the masculine word for 'the' (o).

Where does the word pelo come from, and why does it mean 'over the' here?

Pelo is a combination (contraction) of the preposition por (meaning by, through, or over) and the masculine word for 'the' (o). In Portuguese, we use por (and its contractions) to talk about the means of communication, so 'over the telephone' becomes pelo telefone.