It’s is the Imperfect Indicative Active of plan
I was planning
[size=184]ἐβούλευον[/size]
I think it’s something like
eboole-u-on
eh-boo-leh-ü-on
It’s the [size=184]ευο[/size]
part that’s causing me problems…
As αι is to αυ, so is ει to ευ.
ευ is a simple diphthong, though not one that occurs in most dialects of English, and it should take the time of a single syllable, not two: ἐ‐βού‐λευ‐ον.
(Note to historical linguistics: yes, I know ει wasn’t always *ej.)
Delightfully clear response, William!
I would only add this to expand on William’s explanation: I noticed that you spelled your pronunciation of the letter υ with the German spelling ü, which I assume you did deliberately to capture the fact that the reconstructed pronunciation of υ in Ancient Greek is supposed by linguists to be similar to the French u or German ü (a rounded high front vowel).
And if you know that, then I’m sure you’re also aware – though you may not have thought much about it – that this letter is not believed to have had that pronunciation when it was used as the second letter in a diphthong: in other words, in diphthongs, it is believed to have sounded like a “regular” u (or w), as in αυ and ευ (and even in the [non-spurious] diphthong ου before both the spurious and non-spurious forms of ου fell together as a long “u” sound).
This difference in pronunciation between the two uses of υ were captured by the Romans in their two different ways of transliterating that letter into Latin. As a vowel by itself, the Romans brought it directly into their alphabet as Y, which is why the Romans would spell πολυτροπος as polytropos, with a “y”, but would spell αὐλίς as Aulis, with a “u” – and this remains to this day the conventional way of transliterating Greek, even for those such as Fitzgerald who attempt a more pedantic transliteration than the conventional Roman one.
And this letter continues to be pronounced differently depending on context in Modern Greek: whereas the old rounded front vowel ü has fallen together with iota and eta as the unrounded front vowel , upsilon in a diphthong is now pronounced as an English “v” (or “f” in front of voiceless consonants: ζεύς sounds like “Zeffs” today!)
The diphthong “eu” simply does not exist in English (at least not phonemically, though if you listen carefully to some particularly “upper crust” British accents, you may find that their pronunciation of “o” sometimes approximates this sound 
); so it is particularly difficult for a native English speaker to reproduce. You can get close to the last two syllables of your word by saying “yeah, one” and removing the “y” from the beginning.
Portuguese uses the diphthong ‘eu’ like there’s no tomorrow, so to know how it sounds just listen to some Bossa Nova.
English has the diphtongs ‘au’ as in ‘how’ and ‘ou’ as in ‘no’. Just change the ‘a’ or ‘o’ for a short ‘e’ and you’re in business. Or take the diphthong ‘ei’ as in ‘hay’ and change the ‘i’ for a short ‘u’ (short ‘oo’).