Dear Coworker,

If you are going to take the time to look me up on the corporate messaging system to send me an IM to ask me for my phone number, wouldn't it be just as easy to look me up on the corporate directory and get my phone number yourself?

On a related note, if you then call me to ask me who you should call to solve the problem that you are too lazy to resolve on your own, and I tell you who to call, look their number up yourself. Don't ask me if I have their number so I can look it up and read it to you.

I am not your personal assistant, and I have a very bad attitude to boot.

Warmest Regards,
Beth