i will fix this, but what about the code?
it you want to read a file, then you should also use a File.GotText event to get the text...
also it does not make sense to read an excel file, convert your Excel data into a table in csv format and read that csv file instead
global vairable phonenumbers is the name of a file, not a phonenumber itself, so it does not make much sense to set that filename to Texting1.PhoneNumber
you might want to elaborate, what exactly you are trying to do and do some tutorials to learn the basics
Taifun
A very good way to learn App Inventor is to read the free Inventor's Manual here in the AI2 free online eBook App Inventor 2 Book: Create Your Own Android Apps ... the links are at the bottom of the Web page. The book 'teaches' users how to program with AI2 blocks.
There is a free programming course here Course In A Box and the aia files for the projects in the book are here: App Inventor 2 Book: Create Your Own Android Apps
How to do a lot of basic things with App Inventor are described here: http://www.appinventor.org/content/howDoYou/eventHandling .
Also do the tutorials Our Tutorials! to learn the basics of App Inventor, then try something and follow the Top 5 Tips: How to learn App Inventor
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by 
Taifun.
you can install a custom extension of whatsapp (it's really simple to use)