let
    KoelnerPhonetik = (input as text) as text =>
    let
        _upper = Text.Upper(Text.Trim(input)),
        _replaced =
            Text.Replace(Text.Replace(Text.Replace(Text.Replace(_upper, "Ä", "A"), "Ö", "O"), "Ü", "U"), "ß", "SS"),
        _lettersOnly = Text.Select(_replaced, {"A".."Z"}),
        chars = Text.ToList(_lettersOnly),
        len = List.Count(chars),

        isVowel = (c as text) as logical => List.Contains({"A","E","I","J","O","U","Y"}, c),
        prevChar = (i as number) as text => if i > 0 then chars{i - 1} else "",
        nextChar = (i as number) as text => if i < len - 1 then chars{i + 1} else "",

        encodeChar = (i as number) as list =>
            let
                c = chars{i},
                p = prevChar(i),
                n = nextChar(i),
                code =
                    if c = "H" then null
                    else if isVowel(c) then "0"
                    else if c = "B" then "1"
                    else if c = "P" and n = "H" then "3" else if c = "P" then "1"
                    else if List.Contains({"D","T"}, c) and List.Contains({"C","S","Z"}, n) then "8"
                    else if List.Contains({"D","T"}, c) then "2"
                    else if List.Contains({"F","V","W"}, c) then "3"
                    else if List.Contains({"G","K","Q"}, c) then "4"
                    else if c = "C" then
                        let
                            nIn = List.Contains({"A","H","K","L","O","Q","R","U","X"}, n),
                            pSZ = List.Contains({"S","Z"}, p),
                            ccode = if nIn and (not pSZ) then "4" else "8"
                        in
                            ccode
                    else if c = "X" then if List.Contains({"C","K","Q"}, p) then "8" else "48"
                    else if c = "L" then "5"
                    else if List.Contains({"M","N"}, c) then "6"
                    else if c = "R" then "7"
                    else if List.Contains({"S","Z"}, c) then "8"
                    else null,

                asList =
                    if code = null then {}
                    else if code = "48" then {"4","8"}
                    else {code}
            in
                asList,

        rawDigits = List.Combine(List.Transform({0..len-1}, each encodeChar(_))),
        dedup =
            List.Transform(
                {0..List.Count(rawDigits)-1},
                (i) => if i = 0 then rawDigits{i} else if rawDigits{i} = rawDigits{i-1} then null else rawDigits{i}
            ),
        dedupClean = List.RemoveNulls(dedup),
        finalDigits =
            if List.Count(dedupClean) = 0 then {}
            else
                let
                    head = dedupClean{0},
                    tail = List.Skip(dedupClean, 1),
                    tailNoZeros = List.RemoveItems(tail, {"0"}),
                    rebuilt = {head} & tailNoZeros
                in
                    rebuilt,
        result = if List.Count(finalDigits) = 0 then "" else Text.Combine(finalDigits, "")
    in
        result
in
    KoelnerPhonetik