For Interactive Brokers, I just use their IB Key thing. I have to have my phone handy.
It works quick and easy. But I worry about what happens if I (and my phone) burn up in a car accident and my wife has to deal with it.

Here's how your wife can gain access to your joint Interactive Brokers account if you die and your phone is lost:

1. Account Inheritance (For US Residents):

Designate Beneficiaries: Interactive Brokers offers an "Account Inheritance" feature where you can directly name beneficiaries to inherit your account assets without going through probate. This is the most straightforward method.
You can find this in the Client Portal under User menu > Settings > Account Configuration > Account Inheritance.  
Make sure to add your wife as a beneficiary.
 
Required Documents: Upon your death, your wife will need to provide:
A certified copy of your death certificate.
A signed identification document (driver's license or passport).  
A Non-Probated Estate Action Form with instructions for asset delivery.  
2. Transfer on Death (TOD) (For US Residents):

TOD Designation: Similar to Account Inheritance, a TOD designation allows you to pass your account assets directly to a beneficiary upon your death.  
Required Documents: Your wife will need to provide:
A certified copy of your death certificate.
A copy of her ID.
A Non-Probated Estate Action Form.  
Email: Beneficiaries of TOD accounts should email estateprocessing@interactivebrokers.com for instructions.  

Would having a IB Digital Security Card help in this scenario?

While an IB Digital Security Card is primarily for enhanced security and higher withdrawal limits, it does not directly solve the core issue of your wife accessing the account after your death, especially if your phone is lost.

Here's why:

Authentication Factor: The Digital Security Card is another form of two-factor authentication.1 It generates a unique code that you need to enter along with your password.2 Without the card (or knowledge of how to use it), your wife would still be locked out

Estate Procedures Still Apply: Regardless of the security measures you have in place, the fundamental process of transferring ownership of the account after your death remains the same. Your wife will still need to follow the estate procedures outlined previously (providing a death certificate, identification, etc.).
However, there are some indirect benefits:

Higher Withdrawal Limits: If your wife manages to gain access through the estate process, the Digital Security Card (especially the DSC+ version) would allow her to withdraw larger sums of money more quickly. This can be helpful for immediate needs.
Potential for Shared Knowledge: If you and your wife are both familiar with how to use the Digital Security Card, it might provide her with a slight advantage in understanding the account's security setup.
In summary:

The IB Digital Security Card is a valuable security tool, but it's not a substitute for proper estate planning. The most important steps are:

Designating beneficiaries or setting up a TOD.
Ensuring your wife knows about the account and where to find relevant information.
Having a valid will and engaging in estate planning.
By focusing on these aspects, you can ensure a smoother transition for your wife in the event of your death.