How can I access fields in my javascript?

You can access values of a field via JavaScript using the following syntax:

this.model.get(<field_name>);

Note that you will want to make sure that you do that *after* the data:sync:complete event fires or after render, otherwise you might get an undefined as the data might not yet be loaded.

I'm clearly missing something really basic here, here is the script that I'm executing:

(function(app){

    app.events.on('app:sync:complete', function(){

        app.router.on('route:record', function(module){

            if(module === 'Contacts') {

                app.controller.context.on('button:call_button:click', function(model){

                    var mobilePhone = this.model.get('phone_mobile');

                    console.log("Call button clicked, phone number:" + mobilePhone);

                   // AJAX POST

                });

            }

        });

    });

})(SUGAR.App);

Sorry if this isn't the best place to post code and the error is:

Uncaught TypeError: Cannot read property 'get' of undefined

Thanks for the quick reponse!

I'm clearly missing something really basic here, here is the script that I'm executing:

(function(app){

    app.events.on('app:sync:complete', function(){

        app.router.on('route:record', function(module){

            if(module === 'Contacts') {

                app.controller.context.on('button:call_button:click', function(model){

                    var mobilePhone = this.model.get('phone_mobile');

                    console.log("Call button clicked, phone number:" + mobilePhone);

                   // AJAX POST

                });

            }

        });

    });

})(SUGAR.App);

Sorry if this isn't the best place to post code and the error is:

Uncaught TypeError: Cannot read property 'get' of undefined

Thanks for the quick reponse!

The context for your event callback (essentially, the value of 'this' keyword) is different than it would be if your code was running from a custom Sidecar controller.

You can try using app.controller.context.get('model') to access the current model object in the Record view.