I'm 　working in at Komeda's Coffee in Japan.

Sometimes we have foreign customers there so I practice the, so lately I've been practicing English phrases to userve them in English recently!　Like....

When I serve the foreign customers, I always keep smiling and speaking fluently, but I feel like I forget everyall the phrases that I've practiced so many times!

I'm working in at Komeda's Coffee in Japan.

SometimesRecently we've had we have some foreign customers there so I practice the phrases to serve them so I've been practicing English recently!　Like....phrases! Like:

Recently should go in the front as it's a time adjacent word.

The tense is wrong. This is a description of an ongoing event in the past, so "we have" -> "we have had", "I practice" -> "I have been practicing"

Because "Recently" is the time word in the sentence, "sometimes" needs to be put somewhere else. "Sometimes foreign customers" and "Recently some foreign customers" mean the same thing.

When I serve the foreign customers, I always keep smilinge and speaking fluently, but I feel like I forget everyall the phrases that I practice so many times!

the foreign customers -> foreigners: "the foreign customers" implies there's something specific about this particular group of foreign customers and the people within it. We're just talking about the general label of foreign customers, so we get rid of "the", and "foreigners" is more appropriate.

I always keep smiling and speaking fluently, -> I always smile and speak fluently

I forget every phrases -> I forget all the phrases

I'm working in Komeda's Coffee in Japan.

"I'm working" implies that you are currently at work, to me, with an implication of it being somewhat temporary. "I work" says that that is your job

Sometimes we have foreign customers there so I, so I have been practice theing phrases to serve them in English recently!　Like....

Because you say "recently" at the end, you need to use "have been practicing." You could also say "I am practicing phrases to serve them in English." or "I want to practice phrases to serve them in English."
Also "there" was not wrong, but I think this feels more natural.

How many in your party?"

"How many people are in your party?" (both are acceptable, this is more formal than what you wrote which is pretty casual)

When I serve the foreign customers, I always keep smiling and speaking fluently, but I feel like I forget every phrases that I practice so many times!