I have a string like this:
2234323,23,23,44,433;3,23,44,433;23,23,44,433;23,23,44,433;4534453,23,23,44,433;
3,23,44,433;23,23,44,433;23,23,44,433
7545455,23,23,4
You could do a find and replace on numbers that are seven digits long, to insert a token that you can use to split. The output may need a little extra filtering to get to your desired format.
Output:
array (
1 => '2234323,23,23,44,433;3,23,44,433;23,23,44,433;23,23,44,433;',
2 => '4534453,23,23,44,433;
3,23,44,433;23,23,44,433;23,23,44,433
',
3 => '7545455,23,23,44,433;3,23,44,433;23,23,44,433;23,23,44,433',
)