Dear Sir or Madam,
This letter is to verify that Audrey Sullivan is a full-time employee of Grimes Janitorial Service. Ms. Sullivan is our assistant manager and is currently working out of the state for approximately six months. Our company is expanding, and Ms. Sullivan is assisting with the opening of a new office in Texas. If you have any questions concerning this letter, please contact me at the numbers below.
Signed,
Make sure you list your contact numbers - plural. If you have only one number, then change the last sentence to number.