First you should create a column that supports text. Although they are multiple numbers, the way you want to store, it is impossible to use a numerical field.
CREATE TABLE xxx (
....
sincrozina VARCHAR(255) //defina o tamanho necessário
....);
If you want to add a value in this field, it is necessary to have a record (how you will create it, I don’t know). To increment the field with a value, use the following SQL.
UPDATE xxx SET sincroinza = CONCAT(sincroinza, ",", novo_número) WHERE ....
novo_numero
is the new value you want to enter. To check if a certain number is in this list, you should do it as follows:
SELECT * FROM xxx WHERE sincroniza LIKE %numero_buscado%
Where numero_buscado
is the number you want to verify. If this query returns the record where the list of numbers is, is why the value is in the list.
I only posted snippets of SQL. Since you provided no code, and little information, there is no way to help you with other implementation details, so you will have to adapt these Sqls to your code, to reach the solution.
I edited the question because "phpmyadmin" is not a "database", read this to understand the differences: What is the difference between mysql and phpmyadmin?
– Guilherme Nascimento