How are the mobile numbers formatted? It could be perhaps that the text format used is not recognised by Marketo for these numbers.
Are you using the special character import method? Import a Non-Latin Characters List - Marketo Docs - Product Docs
Importing lists containing non-English names into Marketo may replace accented characters with invalid ones, often squares or non-alphabetical signs when uploaded into marketo.
Use the universal character set (Unicode (UTF-8) which defines the characters included in a majority of the languages of the world. It can work with pages and forms that include a mixture of languages within the same page.