Basically I have a Sql Column named phone, where it contains numbers and letter.
I want to get the max integer value of my phone table, I found that it is possible using
String query = "SELECT MAX(PHONE) FROM db.stb";
String query = "SELECT MAX(PHONE) FROM db.stb WHERE COLUMNNAME=PHONE";
As i mentioned in comments, you should not store two different information in a single column. Consider changing the table structure.
With this structure to get the result, first filter out the rows with alphabet on it. Use
REGEXP to filter the records which has only numeric values. Then take the max value out of it.
SELECT MAX(PHONE) FROM db.stb WHERE col1 REGEXP '^[0-9]+$';
REGEX concept taken from this question : Detect if value is number in MySQL