I added one line to get up to 10 digits starting from the right side. This will remove the leading "1" and I think any country code. (I'm assuming the phone number is in the format for Canada/USA.)

while(<DATA>) {
    s/[^\d]+//g;     # remove non-digit characters
                     # only digit characters remain

    m/(.{0,10})$/;   # find as many as 10 characters,
                     # starting at the right

    print $1,$/;     # print the found digits
}

__DATA__
800-1212
1-800-800-1212
1(800)800-1212
1 (800) 800-1212
1 800 800 1212
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