Most e-commerce platforms let you create orders manually. That way even if you're at a conference or a potential customer calls you you can capture those orders.
While many systems let you create orders manually they don't always let you charge a credit card which kind of defeats the purpose. But even if your e-commerce platform doesn't let you process credit cards if you use Stripe you're in luck. They make processing credit cards really easy.
Adding a Charge
So after you create an order in your e-commerce platform you should have an order number and a total. Once you have those you can open up Stripe and log into your account.
Go to your dashboard.
And then click on Payments which will display all past payments.
Then click New Payment.
This will open up a modal. Where you can enter the order details.
You'll obviously need to fill out all of the credit card details & the order total. But there are a few more fields you should fill out.
The Description is for internal use so I'd put your order number there. That way you have a connection from this payment to a specific order.
You'll also want to fill out the Statement desc. Use something obvious as this is what the customer will see on their credit card statement. If you have multiple online properties or if you meet someone at a convention you may want to use something that describes the products they bought instead of your company name. It should reduce chargebacks.
Don't forget to click More Options. These are useful to prevent fraud. Someone can steal a credit number and call you; so every transaction should go through this.
Make sure to enter all of the billing details which may be separate from the shipping details you received earlier. Ask the customer for billing details if you don't already have them.
The one field you can probably leave empty is the Email for receipt field. The customer should have already received confirmation from your e-commerce platform so there's no need to send them more email.
Once you're done you should see the new charge in the list of payments. And if you click into it you should see the details.
This process requires no additional setup on your end which is awesome. You can take a few phone orders or go to a few conventions and see how this works before adding more complexity to your setup.
Once you decide that something is worth doing then it's worth adding systems & processes to increase efficiency. But until you get a few orders under your belt it's not worth the headache of integrating & maintaining a new system.
Scaling for Conventions
Or for Shopify they have their own Shopify POS system.
Scaling for Phone Orders
If you do get a ton of phone orders I'd look into WooCommerce Phone Orders for WooCommerce.
Just an FYI the company that makes this extension doesn't release their code as GPL. For some developers that's a deal breaker so I wanted to make sure I mentioned it.