There is no evidence to support the idea that Phoenician travelers had sustained contact with early Germanic peoples, and especially not enough to significantly influence German language and writing. There is evidence to show Etruscan, Latin, and Greek influence on Germanic language and writing.
In human language there are often similarities between unrelated languages and these have myriad possible origins. As such, within the realm of linguistics one needs substantial proof to successfully claim a relationship exists between two otherwise unrelated languages.
Either the physical evidence suggests a connection or it doesn't. It is obviously fallacious to insist there could be no contact between Carthaginian and Germanic populations: boats sail between the Baltic and Mediterranean seas all the damn time.
It was only a little time ago that many historians insisted bronze-age tin could not possibly have come from England. ("There's no solid evidence for it!") Then isotope analysis showed that it definitely did. The only correct statement at the time would be that we didn't know whether the tin was coming from England. Accepting the isotopic evidence does not absolve anybody from insisting they knew what they were fully aware they did not know.
In human language there are often similarities between unrelated languages and these have myriad possible origins. As such, within the realm of linguistics one needs substantial proof to successfully claim a relationship exists between two otherwise unrelated languages.