Append Column to row derived from the from three columns

If your original data looks something like:

Then you can use this code:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwtDAwMDcyUtJRcnRyBpLG+sb6RgZGZkCmS2pZZnKqoVKsTrSShZGhgYm5kaUxSCF2dQZgheYgI43NTA1AEtjUWSrFxgIA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [fid = _t, phase = _t, extractDate = _t, deviceName = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{
        {"fid", Int64.Type}, {"phase", type text}, {"extractDate", type date}, {"deviceName", type text}}),

    #"Added Custom" = Table.AddColumn(#"Changed Type", "deviceNamePhase", (x)=>
        List.Transform(
            Text.ToList(x[phase]), 
                each x[deviceName] & "_"  & _  & "_" & Number.ToText(x[fid]))),
                
    #"Expanded deviceNamePhase" = Table.ExpandListColumn(#"Added Custom", "deviceNamePhase")
in
    #"Expanded deviceNamePhase"

to produce:

Hopefully this will point in the right direction.