index is not using? - Mailing list pgsql-performance

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.