You can put the same conversion value for both calls and online form submissions (e.g. $1.00).
Different conversion values only really matter if you are using Maximize conversion value or Target ROAS automated bid strategies for the campaigns. Google will use these values to help determine bidding.
Another reason some people like to put different conversion values is because of the weight of the type of conversion. For example, if more people make appointments over the phone than via the online form submission, therefore more sales by phone than online form submissions, you might want to place a higher conversion value for calls. These numbers can be completely arbitrary but should be based on your data.
Example:
10 calls led to $1,000 in sales, then you can set the conversion value to $100 for calls
10 form submissions let to $100 in sales, then you can set the conversion value to $10 for form submissions
Hope this answers your question!