The rule of thumb is that 100 feet per mile over a full route is a lot of climbing. That doesn't sound like much, since 100 ft/mi is only 1.8% grade, but you have to go down, too, doubling the effective upward grade. And there's usually flat or almost flat sections on a ride, so the grade on climbs is steeper still.

But, there's a difference between a ride with repeated small roller hills, and one with a long climb. Maybe your gps/cellphone is counting every little rise and fall in the road. I get this with routes on ridewithgps.com, where it reports a lot of elevation gain.

For instance, this ride up and over Big Walker Mountain in NC:

link to ridewithgps map has a 1150 foot climb, then a valley ride with small rollers, and a 700 foot climb back up. That's 1150+700=1850 feet, but ridewithgps reports 2356 feet. The valley section of the ride didn't feel like climbing to me. The first climb is 1150 feet in 4.0 miles, or 287 ft/mi (5.4%). That's steep but I can pace myself on a long climb of this grade, and handle it OK.

Road grade is 100 * (elevation change) / (road distance * 5280)

100 feet in 1 mile is 1.8% For me, a noticeable grade.

200 feet in 1 mile is 3.8% Still sitting and pedaling.

300 feet in 1 mile is 5.7% Mostly standing, alternating with sitting. (The amount of standing up depends on my lowest available gear, too)

400 feet in 1 mile is 7.5% Working hard to keep moving.