Pronunciation and characters for 打 110 Without Arabic numerals Memrise provides a phrase that sounds like da yoyo liang. Is yi becoming yo here, and if so under what circumstances would this change occur? Is it just a dialect issue or standard mandarin.
In characters, the phrase is

Dǎ yāo yāo líng
打幺幺零
Dial 1-1-0

「一」is not yāo; rather, a different word「幺」is used. See Pronunciation of 壹 / 一 in Mandarin for the use of yāo.