@juanbretti : You are absolutely right. I am sorry. I overlocked not only that you had already mentioned that link but also that this request is about mobile phones. (Note to myself: Do not answer in here while already dealing with 2 urgent tasks.)
As mobile phones (both iOS and Android) currently do not support this feature its request of cause is justified; although there are already similar ones. Just to name a few see below. There are however more in this forum.
- Search and Copy from Notes Field
- Search within and inside all notes
- Search notes field
- Search into Secure note in Android
On a side note: You can always be the 1st one to cast a vote on your own request.