Simulating a touch on a phone screen without a finger?

A standard touch stylus is designed to work just a human finger on a captive screen. Bonus is that your simulator doesn't start to smell after a couple days.

You have them with hard polymer tip but there's also cheaper ones with a softer, thin layered polymer layer over foam tip. I don't know where you are from, but in Asian electronic malls they start at about 50 cents a pop.

Apple's screens are capacitive touch so you would need to have a 3D servo mechanism to move a sausage or one of those gloves with touch material weaved in to them.

Many food stuffs that contain water (sausage, snacks, string cheese) would work as well if you don't want to spend money on a device engineered to work with capacitive screens for whatever reason.

Programmatically, you would want to connect the iOS device to a Mac and run Xcode Server from Server.app and/or enable UI Automation testing. Then you can script and even code the things you need your "electronic finger" to test. There are many, many videos on the internet covering the test frameworks and how to set this up.