Use this code example to remove the apostrophe that appears before a '+' character when exporting a table with phone numbers.

add_filter( 'frm_export_view_risky_characters', 'remove_risky_characters' );
function remove_risky_characters( $characters ) {
	return array( '=', '@' );
}

If you want to add the apostrophe for potentially risky cells but remove it before the '+' sign for phone numbers, use frm_export_content instead.