keep rows conundrum

You can group by py3_contactnumber choosing to aggregate by count distinct rows and keeping all rows. Then amend the resulting code to take the distinct count of only the py3_consentglobalname column. (The code would like this...)

= Table.Group(#"Changed Type", {"py3_contactnumber"}, {{"_nested", each _, type table [py3_consentglobalname=nullable text, py3_contactnumber=nullable text]}, {"Count", each Table.RowCount(Table.Distinct(Table.SelectColumns(_, "py3_consentglobalname"))), Int64.Type}})

You can now filter the resulting contactnumber count column so that only contacts with a count greater than one are kept.

From there you have to decide which rows you are keeping. If you are keeping only rows with consent as "yes" you could use Table.TransformColumns() to filter the nested tables to keep "Yes" rows. Then expand the tables.
Complete code would look like this...

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WikwtVtJRcvb30zWxMDY2sFSK1cEh6JdPpEKEoKmRiaGFAapuGoohu8bSzMwEtyDCLwYm5ugm4hOLBQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [py3_consentglobalname = _t, py3_contactnumber = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"py3_consentglobalname", type text}, {"py3_contactnumber", type text}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"py3_contactnumber"}, {{"_nested", each _, type table [py3_consentglobalname=nullable text, py3_contactnumber=nullable text]}, {"Count", each Table.RowCount(Table.Distinct(Table.SelectColumns(_, "py3_consentglobalname"))), Int64.Type}}),
    #"Filtered Rows" = Table.SelectRows(#"Grouped Rows", each ([Count] = 2)),
    #"Removed Columns" = Table.RemoveColumns(#"Filtered Rows",{"Count"}),
    Custom1 = Table.TransformColumns(#"Removed Columns", {{"_nested", each Table.SelectRows(_, each [py3_consentglobalname] = "Yes")}}),
    #"Expanded _nested" = Table.ExpandTableColumn(Custom1, "_nested", {"py3_consentglobalname"}, {"py3_consentglobalname"})
in
    #"Expanded _nested"

In this example I started with...

and ended with...

Hope this gets you pointed in the right direction.