Phoenix to Peoria

We dislike interstates and try to do secondary roads. If you have the time that's the way I would go. Here are three options and surprisingly, they are all similar mileages.

Figuring approximately 300 miles/day or 6 hours per day, it would take you 5-6 days of travel but I'd allow more time so you can stop a day or two at various points to just relax. Driving daily wears us out. You can also make variations to these routes.

Also keep in mind that if you're leaving now or later, most public parks will be closed for the season. There should be no problems with RV parks until November. Also keep a watch on the weather.

Taking the interstate directly would put you through some big cities - not fun.

1620 miles - Phoenix/Mesa - take Hwy 60 to Globe; Show Low; Springerville, AZ to New Mexico and I-15. Then cross the highway and pick up 380 east at Socorro, NM to 54 at Carrizozo,NM. Take 54 to I-72 at Griggsville, IL then to I-55 north to Peoria, IL.

1690 miles - Phoenix - take I-10 to Las Cruces, NM. Then US70/82 to Alamogordo, NM and 54 to I-72 at Griggsville, IL to I-55 north to Peoria, IL

1680 miles - via Phoenix and I-17 north to Flagstaff and east on I-40 to I-44 to St. Louis, MO then I-55 north to Peoria, IL

We have been to St Louis several times and this is what we have done.
From Chandler to Dancing Eagle Casino RV Park overnight with hookups $10.00 and 366 miles going thru Payson to Holbrook to get to I 40
From Dancing Eagle either Oasis RV Resort Amarillo 326 miles if you have the time spend a couple of days camping at the bottom of Palo Duro Canyon at Palo Duro Canyon State Park.
Then 226 miles from Oasis RV is El Reno West KOA We like to make this a shorter day since we have had two 300+days and it is a fun stop.
From El Reno West KOA to Springfield / Route 66 KOA is 321 miles
From Route 66 KOA to Casino Queen RV Park in St Louis is 228 miles
and from Casino Queen RV Park to Peoria 166 miles