"Ik mis je"
It's pronounced: "Ik miss ya"
Here are some other ways to say it, depending on the context:
* "Ik denk aan je": This means "I think of you," and implies missing someone.
* "Ik verlang naar je": This means "I long for you," and is a more intense way of expressing missing someone.
* "Ik mis je heel erg": This means "I miss you very much."
Remember that Flemish is a dialect of Dutch, so most Dutch speakers will understand these phrases.