getopts passing value of declared parameter to function

I have function port.sh as stand alone script and i'm wondering if is possible to put this function in the same script where getopts is and pass value of OPT_B into function and get output of it?

        OPT_B=B

        while getopts :a FLAG; do
          case $FLAG in
            b)  #set option "b"
             OPT_B=$OPTARG
              ;;
          esac
        done

    shift $((OPTIND-1))

!!-->> port $1 <<--!! -> OPT_B=$(port $1) ??

    function port()
     {
        if  [ "$1" = 'B' ]; then
        set $1=8000
        echo "declared value: $1"

        elif [[ "$1" =~ ^[0-9]+$ ]] && [ "$1" -ge 1 -a "$1" -le 10000 ]; then
        echo "chosen value: $1"
        else echo "chosen value $1 is not in '1 - 10000'"
        fi
    return 0;
    }