It’s really hard to convey the sounds of spoken Tibetan in written form. Although a system for transliterating the Tibetan alphabet does exist, it is not intended to help with pronunciation and is rarely used outside academia.
What you’ll find instead is a very flexible approach to romanising the Tibetan language, which varies considerably from one end of Tibet to the other, reflecting the many different dialects spoken.
For me, this only came to light when our son, Lobsang, was born and we needed to register his birth. Yeshi told me that he was unsure how to spell the baby’s Tibetan name in English. I was a dictionary editor at the time: much investigation ensued.