Customers form: I would add an unbound combo in the header to find a customer by name
Employees form: same. Also, using one name field rather than separate first and last names is poor practice.
Machine form: Sort the parts list
Parts: What is the purpose of the Part Number? It appears to be unbound.
Sales: Should be form/subform and have search for customer.
Service: add search and sort parts list.
Customer Details: Has report header but no page header. Way too spacey. Header information is repeated for each customer. Report should be reformatted as a simple list.
Customer Phone List: I like it
Relationships: Why is Machine linked to Customer on MachineID--CustomerID? This looks like an error.
Relationships: Service should be related to sales on CustomerID and MachineID rather than to customer and machine separately.
Column names: "Name" is a poor choice (in customers and employees) for a column name since it is the name of a property that is used EVERYWHERE. You will have trouble with this at some point.
Relationships: You have an extra instance of the service table on the diagram. You can delete it.