How can I set up speed dial on iPhone 6 plus, os 9.2.1

ask Siri or Voice Control to dial a contact?

http://help.apple.com/iphone/9/#/iph3c993cbc

...

Use Siri or Voice Control. Press and hold the Home button, say “call” or “dial,” then say the name or number. You can add “at home,” “work,” or “mobile.” See Make requests and Voice Control. For example:

“Call Emily’s mobile”

“Call the fire department”

“Redial that last number”

When voice dialing a number, speak each digit separately—for example, “four one five, five five five….” For the 800 area code in the U.S., you can say “eight hundred.”

In addition to using Siri, you can mark contacts as favorites.

There are two ways to do this:

1. Open the contacts app
2. Tap on the person you want to add a a favorite
3. Tap on add to favorites

OR

1. Open the phone app
2. Tap on the favorites tab at the bottom
3. Tap on the add button in the top right.

Once they are marked as favorites, you can just open the phone app, tap on favorites and make a call. -AJ

It does seem odd that the old concept of "speed-dial" has been forsaken... what if one is kidnapped and can only press one "button" - oh wait! no buttons!

makes perfect sense, really... physical 'keys' are seemingly required for 'speed-dial' UX design

If you can't press one button have the kidnapper charge your phone then while on the charger say, "Hey Siri call 9-1-1.

Search for "Speed Dial" in the App Store.

EXACTLY!!! How can you call this upgrading technology when you're compromising so many things!? Right??

How can I put phone numbers on speed dial

Try the Favorites Widget.

https://www.macrumors.com/how-to/ios-10-customize-contacts/