Text.Contains with lookup

You can do this by 

• Expand the delimited phone numbers into new rows
• JOIN the two tables using a Nested LeftOuter join
• Extract the NAME(s) from the nested table

let

//read in the call table
    Source = Excel.CurrentWorkbook(){[Name="callTbl"]}[Content],
    calls = Table.TransformColumnTypes(Source,{{"Date", type date}, {"Call number", Int64.Type}}),

//read in the client table
    Source2 = Excel.CurrentWorkbook(){[Name="clientTbl"]}[Content],
    clients = Table.TransformColumnTypes(Source2,{{"NAME", type text}, {"PHONE", type text}}),

//split the phones by the delimiter into ROWS
    #"Split Column by Delimiter" = Table.ExpandListColumn(Table.TransformColumns(clients, 
        {{"PHONE", Splitter.SplitTextByDelimiter("/", QuoteStyle.Csv), 
            let itemType = (type nullable text) meta [Serialized.Text = true] in type {itemType}}}), "PHONE"),
    phones = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"PHONE", Int64.Type}}),

//Now join the two tables
    joined = Table.NestedJoin(calls, "Call number", phones,"PHONE","Joined",JoinKind.LeftOuter),

//Extract the matches.
//I'm using Text.Combine since you have multiple clients with the same number in your data
    #"Added Custom" = Table.AddColumn(joined, "CLIENT", each Text.Combine([Joined][NAME],",")),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"Joined"})


in
    #"Removed Columns"