index is not using?

I have created a index
create index leadaddress_phone_idx on
leadaddress(regexp_replace((phone)::text, '[^0-9]*'::text, ''::text,
'g'::text));

But the index is not using.

explain select * from leadaddress where
regexp_replace(phone,'[^0-9]*','','g') like '%2159438606';
QUERY
PLAN
--------------------------------------------------------------------------------------------------------
Seq Scan on leadaddress (cost=100000000.00..100009699.81 rows=1 width=97)
Filter: (regexp_replace((phone)::text, '[^0-9]*'::text, ''::text,
'g'::text) ~~ '%2159438606'::text)

Could anyone please tell me why? I analyzed the table after index creation.