求公式

B2单元格输入数组公式：
BASE(MMULT(LOOKUP(MATCH(MID(A2,COLUMN($A:$D),1),MID(A2,COLUMN($A:$D),1),),COLUMN($A:$D))+9,16^(4-ROW($1:$4))),16)

适合老版EXCEL（没有CONCAT的）：

还是用BASE，但排列正确了。。
定义一个名称：AAAA=LOOKUP(MATCH(MID($A1,COLUMN($A:$D),1),MID($A1,COLUMN($A:$D),1),),COLUMN($A:$D))
B2公式=BASE(MMULT(TRANSPOSE(MMULT(N(TRANSPOSE(AAAA)>=AAAA),1/MMULT(N(TRANSPOSE(AA
AA)=AAAA),ROW($1:$4)^0)))+9,16^(4-ROW($1:$4))),16)

更短：IF(COUNT(1/FREQUENCY(VALUE(MID(A2,ROW($1:$4),1)),VALUE(MID(A2,ROW($1:$4),1))))=4,"ABCD",SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A2,LEFT(A2),"A"),LEFT(SUBSTITUTE(A2,LEFT(A2),"")),"B"),LEFT(SUBSTITUTE(SUBSTITUTE(A2,MID(A2,1,1),""),LEFT(SUBSTITUTE(A2,MID(A2,1,1),"")),"")),"C"))

又改了一下：IF(COUNT(1/FIND(ROW($1:$10)-1,A2))=4,"ABCD",SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A2,LEFT(A2),"A"),LEFT(SUBSTITUTE(A2,LEFT(A2),"")),"B"),LEFT(SUBSTITUTE(SUBSTITUTE(A2,MID(A2,1,1),""),LEFT(SUBSTITUTE(A2,MID(A2,1,1),"")),"")),"C"))

=VLOOKUP(SUM((MID(A2,{9,10,11,10,11,11},1)=(MID(A2,{8,8,8,9,9,10},1)))*2^{1,2,3,4,5,6}),{0,"ABCD";2,"AABC";4,"ABAC";8,"ABCA";16,"ABBC";22,"AAAB";24,"ABBA";32,"ABCB";36,"ABAB";42,"AABA";64,"ABCC";66,"AABB";76,"ABAA";112,"ABBB";126,"AAAA"},2,)

做这个，VBA函数省事

BASE的不需要名称：BASE(MMULT(TRANSPOSE(MMULT(N(MATCH(MID(A2,COLUMN(A:D),1),MID(A2,COLUMN(A:D),1),)<=MATCH(MID(A2,ROW($1:$4),1),MID(A2,ROW($1:$4),1),)),1/MMULT(N(MATCH(MID(A2,COLUMN(A:D),1),MID(A2,COLUMN(A:D),1),)=MATCH(MID(A2,ROW($1:$4),1),MID(A2,ROW($1:$4),1),)),ROW($1:$4)^0)))+9,16^(4-ROW($1:$4))),16)

@zipall

let
源 = Excel.CurrentWorkbook(){[Name="表1"]}[Content],
转换 = Table.AddColumn(源, "转换", each Text.Combine([尾号=Text.ToList(Text.End(Text.From([手机号码]), 4)),唯一=List.Distinct(尾号),偏移=List.Transform(尾号,each Character.FromNumber(List.PositionOf(唯一,_)+65))][偏移]))
in
转换

短了一些:
IF(COUNT(1/FIND(ROW($1:$10)-1,A2))=4,"ABCD",SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A2,LEFT(A2),"A"),LEFT(SUBSTITUTE(A2,LEFT(A2),"")),"B"),MID(A2,SMALL(IFERROR(FIND(ROW($1:$10)-1,A2),5),3),1),"C"))