Well, my initial intention was to close this question exactly for the reasons mentioned by @Quassnoi - it looks like you are confusing following concepts - "звук" (a sound) and "фонема" (a phoneme). In phonology phoneme is a unit of sound that distinguishes one word from another in a particular language. There's some argument about this, however usually in order treat something as a phoneme you need to have a pair of words differing in this phoneme (one has it, one does not, like "дом" / "том").
I'm not aware of such three letter phonemes in Russian. Russian alphabet is quite phonetic, apart from palatalized consonants, all most frequent phonemes are expressed with a single letter.
We, just for fun, can examine following beasts: palatalized geminates, that is, softened doubled consonants. We do have some geminates in Russian, compare "коса" and "касса". Finding palatalized one (especially spelled with three letters, otherwise one can use dialectal "дрожжи" as an example) is a bit tricky, grepping a dictionary will help you to find some extremely exotic words like каттьерит (a metal), гюиссье (a historic term for special kind of guard), шоконнь (a dance) however with "л" you'd be lucky enough to find a a couple of more frequently used words, like "балльность", "тролль".
It's not a phoneme in Russian by any stretch of imagination, moreover, unlike the geminated "с" geminated l is quite exotic for a Russian native speaker. I can imagine and I can pronounce "тролль" myself with a long soft consonant however it would be really untypical.
But palatalized geminates is the closest I can think of.
UPD: today I woke up and realized that there's even a ль/лль pair in Russian - "коли" and "колли" )