I want my iPhone to RING if someone calls me 2-or-more times in a row... (even if phone is on silent)

The mute switch is a dumb switch; it’s all or nothing. That’s why your phone has Do Not Disturb, that supports the option you need (and many others).

Do Not Disturb setup has been made much more flexible, but this has come at the cost of much more complication. To get it working again, do these steps ONCE:

• Tap Settings
• Tap Focus
• Tap on any Focus settings that you will never use and remove them (you can add them back later if you change your mind, and even create new, custom ones)
• Tap Do Not Disturb
• Tap People
• Tap Allow Notifications From
• If anyone is listed who should not call you when DND is on delete them; if you don’t want any calls from anyone, any time, delete all people
• Tap the dropdown next to Allow Calls From and choose Allowed People Only
• If desired, turn on Allow Repeated Calls
• Optionally, tap on Apps, then Allow Notifications From and don’t add any apps.

All of the above is a one-time setup. After that, turn DND on or off with the Control Center Focus button. You can optionally set one or more schedules by going to:

Settings/Focus/Do Not Disturb/Set a Schedule.

You can allow repeated calls or folks access during do not disturb: Use Do Not Disturb with Focus on your iPhone or iPad – Apple Support (UK)

If there is a specific individual you need to have the phone ring for, regardless of ANY settings including focus or the physical ring/vibrate switch, open their contact record, tap edit, go down to ringtone and select that. At the top of the list of tones is a switch for "Emergency Bypass". Turn that on. You can do the same thing for the messages tone.

Note that this will ALWAYS bypass your focus and mute settings. They will not need to call repeatedly for it to get through.