I checked Google Maps and found a few routes that should bring you into Phoenix in about 20-21 hours. The run across Nevada is an hour shorter but offers fewer places to stop. The I-5/210/10 run is at least an hour longer, depending on traffic, time of day, and day of the week, but will give you more lodging, food and rest options. If you leave I-5 around Lost Hills or Buttonwillow, head East through Bakersfield to Needles then S. to I-10, you can avoid the route that skirts the northern edge of Los Angeles. Los Banos is about 11+ hours S of Portland (plus stops) and could be a good place to spend the night if you're up to it. If you keep to the right lane except to pass and give the trucks plenty of room, you'll be following the accepted norms. I find that people who spend all their time in the fast lane may tempt faster drivers to undertake potentially dangerous moves to get around them. Water, non-sugary snacks, and cruise control can minimize fatigue. Have a safe trip.
I just did this drive. Come down to Bend, head over to Nevada, come south through Tonapah, head towards Hoover Dam, then come south through Kingman to Wickenburg and to Phoenix. If you have AAA, they will map out a route. You may consider taking 3 days to do this drive... you'll go through some pretty remote areas. Another idea is to take I-5 to Sacramento, then head towards Tahoe and Vegas and Kingman, etc. Do not take I-5 all the way to LA... I made that mistake!