how to select exact 7 or 10 world in oracle using regular expression

I am working on below query, I am expected to select exact 7 or 10 digit values columns using regular expression, I have used express in regexp_like() function of oracle, but its not working, please help

Query :

select * from 
(select '1234567CELL' "a" from dual
union
select '123CaLLAsasd12' "a" from dual
union
select 'as9960488188CELLas12' "a" from dual
union
select '1234567' "a" from dual
union
select '9960488188' "a" from dual
union
select 'asdCELLqw' "a" from dual) b
where b."a" like '%CELL%' and   regexp_like(b."a",'^(d{7}|d{10})$');

Expected output

"1234567"

"9960488188"

as above two rows, please check