The car comparison is pretty dumb, but whatever. Whatever you decide to do, you're doing to need some kind of a transmitter that will talk to the garage door and receive a signal from the iPhone, perhaps via the internet. It could be done, but my guess is that anyone with the expertise to create such a product isn't interested because the key pad thing already exists and is cheap.

I have a fingerprint scanner for opening my garage door. Works pretty well, and it was only a little more than a keypad. There is a standard for opening garage doors; manufacturers try hard to hide that from you, but they want the openers built into cars to be able to open their doors so they follow the standard.

I've been using a programable keychain opener for years now. I stuck a small piece of Velcro on the side of my stem, and a mating Velcro on the back of the opener. I can open the garage door from about 100' or so when arriving home.

Here are a variety from Amazon:

https://tinyurl.com/6ho6x7d

I use a keypad. I get off my bike about 5 feet inside the garage anyway, so the few seconds I save by riding in doesn't warrant an overly complicated solution.

I agree with everyone on the wireless keypad. However if you really want to use your iPhone there is a way. I can do it as part of an overall home automation system. It will be quite costly, especially if that is the only function you want.

Goto Homeseer. You will need a windows pc running the software 24/7, some hardware interfaces, like X10 or similar wired to your garage door button. They have an iPhone app that you can customize to control whatever is on your system.

Again, I have all that after years of building it up. I can open the garage door with my phone from anywhere in the world. But after biking, I get off my bike and use the cheapy wireless garage door keypad.

I've been called pessimistic before, so here's my thoughts on the OP's obsession to find an app for iPhone (at least say you have Verizon and not paying ATT):

-What happens when the phone fails you? Drop it one too many times, battery dies, screen goes out...
-You must live in and ride in warm weather. I couldn't operate my old touchscreen phone while wearing gloves.
-While you're fiddling with your gizmo, what are you going to do if some suicidal squirrel decides to make a kamikaze run at your front wheel?

There are a number of home control systems of varying complexity, cost, and functionality out there. However, I would classify all of them as "projects" unless you hire an installer which will be $$$$$.