The second parameter is the field which contains the form ID to which it belongs and its own ID so you can target a specific form/field like so:
add_filter( 'gform_other_choice_value', function( $placeholder, $field ) {
// Update "123" to your form ID and "4" to your field ID.
if ( $field->formId == 123 && $field->id == 4 ) {
$placeholder="Your custom placeholder";
}
return $placeholder;
}, 10, 2 );