Hard to say. If you ask for mitigation you are admitting the infraction and it will be found committed, though you might get a break on the cost of the ticket. It will go on your history and may adversely affect your insurance rates.
There isn't enough information here to see if there is a basis to contest the ticket. If it is dismissed, then it won't show up on your history at all. However, tickets are routinely dismissed because of technical problems - such as the ticket not be filed on time, the officer not making a statement,etc. The fact that you were not cited for the speed is interesting.
Chris Mainard in Seattle is a ticket genius. You might want to contact him. Hope this helps.
With all due respect to my colleague, I disagree with her answer.
First, a Washington cell phone ticket is not a "moving violation" that will affect your insurance rates. It will go "on your record" but is no different than a seat belt ticket or driving with expired tabs. Neither contesting the ticket nor paying it will result in increased insurance rates.
If you are hoping to keep the ticket off your record, you need to contest it. That is the only way to make the State prove their case (they have the burden to do so). Contesting the ticket doesn't cost anything -- unless you hire a lawyer. If you lose, the court doesn't penalize you for having the hearing, you would just end up paying the same fine you would have in the beginning.
If money is more important to you than a clean record, your should mitigate. The ticket will go on your record, but you will probably get the fine reduced.
I am sorry you got this ticket but it is much less serious than a speeding ticket or other moving violation. Good luck.
Washington Traffic Defense