Telephone line on the PC or laptop?

I'm self-employed and use a program and make phone calls via phoner.

every time I want to reach a customer it shows me that it is occupied and when I reach the customer later (about 5 minutes) he tells me that the item has already been sold.

what can I do to make the connection from Phoner faster so that the connection to the customer sounds in a few seconds as possible (1-2 seconds).

Do I have to change anything about my wiring?

Are there any better telephony devices than phoners?

Are there certain routers that are suitable for telephony where the connection is established faster?

can I install a network card for telephony?

for info: I know the ISDN was the fastest line to establish the connection

I hope someone can help me or has an idea for me.

What kind of router are you currently using?
What speaks against it using a landline / cellular phone instead of using a PC?

The Fritzbox seems to support Phoner too. Maybe you could try it with a Fritzbox, you can get halfway up-to-date models used on eBay at a reasonable price. Alternatively, you could also connect telephones, for the Fritzbox there's also believe, if I remember correctly, programs with which you can choose from the PC on the phone.

https://www.wintotal.de/telefonieren-vom-pc-mit-headset-ueber-die-fritzbox/

I also do it via the Fritzbox, also with a forwarding to mobile is recommended. You can also see the missed calls via the Fritzbox on the mobile phone.

Without fritzbox you can't use phoner I think I have the Fritzbox7490 at the moment.

I have a search program on the PC for certain things and am not the only one who uses it, so typing in the number on the network is bad. I click on the number on the pc and then he dials.